Device for producing high speed air projectiles or pulses

ABSTRACT

An assembly for producing air projectiles. The assembly includes a driver with an attached converging nozzle. The driver includes a flexible diaphragm and is responsive to an electrical control signal to displace the flexible diaphragm from a first position to a second position. In one embodiment, the driver is an audio speaker driver such as a woofer and the diaphragm is a speaker cone or diaphragm. The nozzle has an inner bore or chamber that converges from a first size at a first end proximate to the driver to a second, smaller size at a second distal end. The second end of the nozzle may include a planar muzzle extending perpendicular to a central axis of the bore and including an outlet smaller than the diaphragm diameter. The driver has a rapid response to control signals such as less than about 20 milliseconds to produce a projectile at the muzzle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to air cannons and other devices that operate to generate air rings, air and smoke vortices, and puffs of air, and, more particularly, to a device, and method of operating such a device, that quietly produces air projectiles or pulses that travel at relatively high speeds while generally retaining their shape, e.g., a projectile, slug, or pulse rather than rapidly dispersing.

2. Relevant Background

Air “cannons” are commonly used to prevent buildups of material and to improve material flow in industrial settings. Generally, these industrial-use cannons use an accumulator or tank to store a quantity of pressurized air from a compressor or other source. A large-flow, fast-acting valve is then used to selectively release a quantity of the air through a nozzle or other outlet. These air cannons provide an effective technology for use in removing possible bottlenecks in piping or other material processing equipment to boost flow.

However, there are many applications where the industrial air cannons are not well suited. For example, theme or amusement parks often include rides or attractions in which it is desirable to provide a puff or pulse of air that can be directed at a guest or otherwise used to achieve a special effect such as moving an object without mechanical devices. Industrial air cannons are undesirable in these settings because they are generally large and bulky, which leads to space constraints on where the air cannons can be positioned. The typical air cannon is also very loud, and this can alter or ruin the overall effect of a ride or attraction. As a specific example, many attractions or shows within parks place a 90 decibel or similar limit on how loud accessory equipment can be and still be masked or covered by the sound (e.g., soundtrack or music) of the attraction. Industrial air cannons often exceed this limit while operating to refill the accumulator and nearly always will exceed this attraction sound limit when the fast operating valve is opened to “fire” the cannon. Hence, there remains a demand for a quieter and smaller device for providing a pulse or slug of air that can be directed or aimed to produce a desired effect.

Vortex or ring launchers are also used in some applications. These ring launchers typically use a piston or other mechanical ramming device to move a volume of air through a chamber and output a ring or vortex of air. In many cases, smoke or dust is provided in the chamber such that the launcher produces smoke rings. Ring launchers are useful for generating slow moving and long lasting smoke ring effects, but these launchers are not suited for shooting a volume or slug of air across a room to achieve an almost immediate effect. In some applications, attraction or ride designers wish to have a guest feel a blast of air in real time such as when a ride car quickly passes a particular point in a ride or when a particular scene is shown in a movie (e.g., in a 4D attraction). The designer further may need to quickly deliver a pulse or slug of air at a location 10 to 20 feet or more from the launcher's outlet, but the ring launchers produce rings that cannot be felt (e.g., often only seen) at this distance due to dissipation of the ring and that require significant amounts of time to travel this distance. A slow moving ring of air fails to provide the result or effect needed in these cases.

There remains a need for an improved air cannon or device for producing air projectiles that travel at relatively high speeds and that do not dissipate rapidly after being created or launched. Preferably, such an air projectile device would be less bulky than existing industrial air cannons and would be quieter during discharge and between discharges.

SUMMARY OF THE INVENTION

The present invention addresses the above problems by providing an air projectile assembly that provides a very fast response to a control signal to shoot or discharge a high speed volume or slug of air. In one embodiment, the invention combines a driver of an audio speaker (which may be also known as a loudspeaker, a voice coil loudspeaker, or the like) with a converging nozzle. For example, the driver may be a large diameter woofer or voice coil device for a loudspeaker. The converging nozzle is sealed to the loudspeaker driver and includes a planar end piece or muzzle at the distal end that has a smaller outlet or opening (e.g., less than about 6 inches in many applications). A driver is selected with a large throw such as an excursion of 1 to 3 inches or more of its flexible diaphragm or cone (as typically measured peak to peak or, in some cases, rest to peak). In some embodiments, two or more drivers or loudspeakers are mounted on a manifold such that their excursions and air displacement may be combined with concurrent firing (or for firing in series). The multiple drivers may feed a common exit to increase the electrical power handling or increase the volume of air that is displaced. A control signal is selectively provided to the driver to cause the driver to move through at least its forward throw (e.g., toward the nozzle or away from the driver itself). The control signal may have a short duration or cycle to cause the displacement of the driver's cone to occur rapidly such as less than about 100 millisecond and typically less than 20 milliseconds. This causes a rapid displacement of air next to the cone within the nozzle's bore or chamber, which results in pressurization of the air in the nozzle bore and a projectile to be expelled or shot out the opening in the muzzle or distal end of the converging nozzle.

Tests show that a slug or projectile of air can be rapidly transmitted across a distance of 10 to 30 feet (e.g., in less than about 1 second) by using a high-power woofer (e.g., a woofer rated at 500 to 1000 Watts RMS) for the driver that has a diaphragm diameter of about 13 inches along with a 13-inch long nozzle that converges at a slope of 5 to 10 degrees and has a muzzle with a 1 to 3-inch diameter round hole or outlet. The assemblies of the invention are much quieter and less bulky than existing industrial air cannons, are less expensive to produce, and require little or no maintenance. Further, the use of all or portions of audio signals or waves (e.g., such as may be produced with standard audio tone or wave generation software and the like) allows easy control of the driver and the production of differing projectiles as the driver responds differently based on the control signals, which allows projectiles of differing size and speed to be transmitted simply by sending differing control signals to the driver. There are many possible driving electrical waveforms. The wave or waveform can be varied to alter the duration, velocity, and/or force of the ejected air pulse or projectile. One method for operating the driver is to ramp the waveform from zero to maximum to drive the voice coil of the driver to one mechanical limit and then to reverse the polarity to suddenly propel the cone or diaphragm to the other mechanical limit of the loudspeaker. This technique generally displaces the maximum or substantially the maximum volume of air for which the particular loudspeaker is capable based on its design.

More particularly, an air projectile assembly is provided that includes a driver and a nozzle attached to the driver such as with a relatively air tight, mechanical seal. The driver (or drivers provided in a manifold in some embodiments) includes a flexible diaphragm and is responsive to an electrical control signal to displace the flexible diaphragm from a first position to a second position. In one embodiment, the driver is an audio speaker driver such as a woofer and the diaphragm comprises a speaker cone or diaphragm. The assembly further includes a nozzle connected to the driver (such as adjacent to the basket or frame about the suspension when the driver is a speaker driver). The nozzle typically is a converging nozzle with a bore or chamber that converges from a first size at a first end proximate to the driver to a second, smaller size at a second end that is distal to the driver. For example, the slope or angle of convergence maybe less than about 20 degrees such as in the range of 5 to 10 degrees. The nozzle may have a length that is selected to provide a desired volume and based on the size of the diaphragm, e.g., to have a length selected from the range of about 50 percent of the diameter of the diaphragm (as measured across the attachment to the suspension in the speaker driver embodiment) to about 150 percent of the diaphragm diameter. In some cases, the length of the nozzle is selected to approximate the diameter of the diaphragm to provide a volume of air in the bore that can effectively pressurized by the displacement of the diaphragm. The second end of the nozzle may include a planar muzzle extending perpendicular to the central axis of the bore and including an outlet that is much smaller than the diaphragm diameter (e.g., less than about one half of the diaphragm and more preferably 10 to 30 percent of the diaphragm diameter such as 2-inch diameter hole when the diaphragm is about 13 inches in diameter). For example, the diaphragm diameter may be selected from the range of up to 24 inches (such as 8 to 20 inches or the like) while a circular outlet in the muzzle may be selected from the range of 0.25 to 12 inches depending on the desired output/outlet velocity with smaller outlets providing higher speed projectiles. The driver preferably has a rapid response to the control signal such as less than about 20 milliseconds, and the distance from the first position to the second position of the diaphragm may be 0.5 to 4 inches in some embodiments.

According to another aspect of the invention, a system is provided for selectively generating air projectiles that travel rapidly into a target environment (e.g., a gaming environment, an area where guests or clients pass or located relative to a show or attraction, or the like). The system includes an air projectile assembly with a power amplifier amplifying electrical control signals, a driver with a flexible membrane that responds to the control signals by moving a central portion of the membrane so as to displace a volume of air, and a converging nozzle with a chamber containing the displaced volume of air. The nozzle also includes a muzzle or end with an opening that is smaller than the diameter of the membrane, and the muzzle opening is aimed at the target environment. The system further includes a controller that transmits the electrical control signals to the power amplifier in response to detected triggering events, which results in the air projectiles being discharged or expelled out of the muzzle opening based on corresponding electrical control signals. The driver in some cases is an audio speaker driver such as a woofer and the electrical control signals transmitted by the controller are audio signals or waves such as signals generated by the controller in response to the triggering event or retrieved from memory that is accessible by the controller. In some embodiments, some of the electrical signals take on differing forms such as differing frequency and/or differing duration and in response, the air projectiles generated based on these differing forms of signals vary such as in speed, in size/volume, or the like. The controller may aim or shoot the air projectiles in differing (e.g., random-appearing) directions from the muzzle opening (or along differing target lines relative to a central axis of the opening/chamber) by maintaining the time between successive electrical control signals below a predefined threshold (such as less than about 10 seconds and more typically less than about 5 seconds). The triggering events for the system may include occurrences in a video game, and in these cases, the air projectiles may follow a target line toward a guest or object in the target environment. Further, the targeted guest or object may be more than 5 feet away but the projectile still reaches the guest or object quickly such as in less than about one second or a fraction of a second.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a system (e.g., a ride, attraction, show, game or the like system) incorporating an air projectile device according to one representative embodiment of the present invention;

FIG. 2 is a side view of a portion of an air projectile device or assembly of the invention such as may be used in the system of FIG. 1 illustrating an exemplary driver and nozzle that may be combined to produce air projectiles;

FIG. 3 is a cutaway perspective view of an air projectile device, similar to that shown in FIG. 2, illustrating further the components of the device including a flexible cone or diaphragm that is moved or driven by a voice coil to displace air in the chamber or bore of the nozzle;

FIGS. 4A-4C illustrate end views of embodiments of the muzzle end of nozzles for use in the air projectile assemblies of the invention;

FIG. 5 is a flow chart of operating a system with an air projectile assembly of the present invention to selectively produce/fire air projectiles; and

FIG. 6 is a perspective view of another air projectile device or assembly of the invention including a manifold and multiple loudspeakers or drivers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Briefly, the present invention is directed to air projectile devices that utilize a driver such as a bass audio speaker or woofer combined with a converging nozzle. The driver is triggered or controlled by a pulse such as an audio or other electrical signal that is typically amplified so as to cause a relatively large flexible membrane or cone of the driver to rapidly move or travel through its throw (e.g., at least the forward or outward portion of the driver's excursion or throw). The driver membrane or cone is provided proximate to the larger end of the nozzle and displaces a volume of air in the bore or chamber of the nozzle that is forced through the outlet in the smaller end of the nozzle toward a target. The nozzle acts to concentrate the air into a projectile or slug that is expelled at high velocity out the small diameter outlet (e.g., less than about 5 inches such as about 2 inches diameter circular hole) in the nozzle's muzzle, which may planar or, in some cases, frustaconical (i.e., a cone with its top cut off by a plane), semi-spherical, or other shape. The overall size of the projectile assembly may be relatively small, with one embodiment being about 2 feet in overall length and less than 1.5 feet in outer diameter, so as to improve on the bulkiness of existing mechanically actuated air cannons. The projectile assembly is also generally much quieter than existing cannons, with the driver typically putting out a single “thump” at decibel levels well below that produced by air cannons and, additionally, there is no noise produced by the assembly between discharges. The assemblies of the present invention also can be assembled at reduced cost without the need for expensive quick action valves and without the need for an air compressor and pressurized air storage. The air projectile assemblies may utilized as standalone devices or within systems in which the projectile system is part of an overall effect such as an amusement park attraction or an arcade game or theater (e.g., a 4D or multiple sense game or show). The use of the term “air” is intended to be a generic term for any gaseous projectile including gases differing from air and air that includes dust or smoke particles.

An exemplary system 100 is shown in FIG. 1 in which an air projectile assembly 140 of the present invention may be implemented to achieve a desired effect. The system 100, for example, may be an effect system or ride/attraction system provided at an amusement or theme park or in a video or other arcade, and a part of the attraction or game or other entertainment may be to cause air projectiles to travel rapidly into a target environment 160. The air projectile assembly 140 may be configured to target or aim the air projectiles direct toward or to the vicinity of a guest/user 164 within the target environment 160 or alternatively, may be used to strike or pass near to an object or structure 166 to cause the object or structure to move, vibrate, or otherwise react in a desired manner to create a desired effect (e.g., to cause a skeleton to suddenly shake, to make a mobile or chimes rattle, or the like). The system 100 may have many other applications such as to produce an effect during a video or arcade game. For example, a game may display objects (e.g., balls, bullets, or the like) flying toward a guest 164, and air slugs 150, 152, and/or 154 may be shot from the assembly 140 into the environment 160 where they may strike or pass by the guest 164 or the object 166. In this way, the guest 164 is provide a third or fourth sense during the game that is timed or synchronized with occurrences or action in the game such as with video or animation generated by the game controller. Alternatively, the environment 160 may be an attraction such as a ride or show in which it is useful to have the air projectiles or slugs 150, 152, 154 pass or hit the guest 164 in response to occurrences on the ride or in the show or based on a location of the guest 164 in the environment 160. The assembly 140 may also include a scent source 149 (such as an oil, waxed disc, or the like adjacent or within the nozzle 146) to provide a scent with the projectiles 150, 152, 154 into the environment 160. The assembly 140 may also be used to provide pulsed air (e.g., hot or cool air may be provided at an inlet to the nozzle 146) of differing temperature to the guest 164. Additionally, the projectiles 150, 152, 154 may include smoke, dust, or the like such that they are visible, and the assembly 140 can be used as a high speed smoke “ring” generator in certain cases.

To provide such applications, the system 100 includes an attraction/game server 110 with a processor 112 that runs or provides an attraction/game controller 114. The server or client device 110 may take many forms such as a server, desktop computer, a personal computer, a laptop computer, notebook computer, or other programmable electronic device. The controller 114 may be provided as hardware and/or with software such as code that is run by processor 112 to generate game effects and to at least periodically transmitting electrical control signals or pulses on line 130 to the air projectile assembly 140. More typically, the controller 114 acts to transmit the electrical control signals 130 as part of the attraction or game being provided by the controller 114 or by another device(s) (not shown)+As discussed above, the controller 114 may transmit the signals on connection 130 in response to a scene displayed in a film clip, in response to activity in a video or arcade game, or based on another triggering event.

The air projectile assembly 140 receives the electrical control signals on line 130 that is typically (but not in all cases) to a power amplifier 142 that amplifies the signal. The amplifier may take many forms and have differing capacities to practice the invention. In some embodiments, the amplifier 142 takes the form of an amplifier used with audio speakers. The amplifier 142 provides the amplified signal to the driver 144 which responds to displace a volume of air in the attached nozzle 146 to force the displaced volume of air out of the outlet 148 as an air slug or projectile 150, 152, 154 that, as shown, travels to or is targeted into the target environment 160. In some embodiments of the invention, the driver 144 is an audio speaker driver such as a tweeter, a midrange, or a woofer and the cone or diaphragm of the speaker driver moves in response to the amplified signal to displace a volume of air in the nozzle 146 to create the projectile 150, 152, or 154. The nozzle 146 is typically attached with an airtight seal to the driver 144, although in some cases an inlet port (not shown) may be provided such that the displaced air may be replenished more quickly rather than just through port or outlet 148. Exemplary driver and nozzle configurations are discussed in more detail with reference to FIGS. 2-4.

As shown, the slugs or projectiles 150, 152, 154 may travel in differing paths. This may be achieved by having a nozzle or outlet that can be variably targeted such as by control by the controller 114, but in more typical cases, the variable travel paths of slugs 150, 152, 154 are achieved by firing the projectile assembly 140 without a long delay between shots or discharges. Experiments performed by the inventor have shown that when the assembly 140 is discharged or fired with less than about 20 seconds between discharges and more preferably less than about 10 seconds between discharges a first slug or projectile 150 will travel on a path substantially along the axis of the nozzle 146 (i.e., when the outlet 148 is placed centrally on the muzzle or narrow end of the nozzle 146). However, subsequent projectiles 152, 154 will travel along or be targeted differently. In many applications, this more random pattern of the discharged projectiles 150, 152, 154 is desirable as it makes it more difficult for the guest (e.g., a game player or the like) to anticipate or to grow tired or bored with the effect. When it is again desired to fire at an aligned or specifically targeted object such as with slug 150, the controller 114 can simply wait past the threshold time period (such as longer than about 10 to 20 seconds) and the next projectile 150 will be more accurately targeted or directed (e.g., when air is completely replenished in the nozzle 146 and/or when “turbulence” in the nozzle is gone or below a particular level).

As discussed, the driver 144 may be a loudspeaker driver. A woofer or subwoofer is particularly desirable due to the larger size of the cone or diaphragm (e.g., flexible membrane) and greater throws or excursions that produce greater volume air displacements. For example, a 22-inch woofer with a 4-inch excursion or throw (e.g., 2 inches forward and 2 inches backward) may be used as the driver 144 to obtain a projectile with a size or volume (e.g., about the size of a baseball or larger) that is useful for many effects. When a speaker driver is used, the control signals 130 may be audio signals transmitted by controller 114 and amplified by amplifier 142. In this regard, the attraction/game server 110 may include a control signal generator 118 such as audio signal generation program or software that can be used to create signals 124 that are stored in memory 120 for later retrieval and transmittal by controller 114 to amplifier 142 in the projectile assembly 140 as shown on line 130. The control signal generator 118 may be accessed by an operator of the server 110 via a user interface 116 (e.g., a GUI or other I/O devices such as a keyboard, a mouse, a monitor, and the like). The operator may use the control signal generator 118 to create a variety of control signals 124 and the controller 114 may transmit differing ones of the signals 124 based on a desired effect.

In one embodiment of the invention, the control signal 124 is a simple sine or square wave with a short duration. The short duration or cycle is preferable because want very fast response, e.g., a response measured in the milliseconds. For example, the duration of the wave may be less than about 100 milliseconds and more typically less than about 20 milliseconds such as about 16 milliseconds or less. This short wave duration results in a very rapid movement of the driver or its flexible membrane to cause the air displacement, which produces a relatively high speed projectile that in some embodiments is able to cross a distance to a target, d_(TARGET), that is typically 40 feet or less in a short time period (such as less than 1 second). The frequency of such a wave may also be selected over a large range to effectively practice the invention. In one case, a frequency of less than about 40 Hertz is used such as about 32 Hertz but this is not required. Further, the control signal may use the entire wave signal (a backward and forward throw or stroke) or Just the positive portion or the portion that causes the driver to move forward (i.e., toward the nozzle or into the nozzle's chamber or bore). As will be appreciated, the use of a driver 144 that does not require pressurized air storage and that can be triggered at a speed measured in the milliseconds in response to electrical (e.g., audio) control signals provides an operator of the assembly 140 significantly more and differing control by providing control over the timing of the discharging of projectiles (e.g., by selecting when the signals are sent), control of the size of projectiles (e.g., by changing the power supplied by the amplifier 142), control of the speed of the projectiles (e.g., by changing the wave cycle time or duration), and control over the direction of the projectiles (e.g., by varying the length of the delay between successive discharges the targeting can be made random or less predictable).

The acceleration of the cone is determined by the well-known equations: F=ma and F=BLi or a=BLi/m where B=magnetic flux in the voice coil gap in Teslas; L=length of wire in voice coil gap in meters; i=the driving current from the amplifier in amperes; and m=the moving mass of the loudspeaker (e.g., typically the combined mass of the voice coil, voice coil former, cone, dust cap, and half the mass of the suspension components). The shape of the output, projectile, or pulse is determined by the driving waveform and the acoustic reactances and resistances of the cavity between the loudspeaker cone and the exit opening.

FIG. 2 illustrates a side view of an embodiment of an air projectile assembly 200 of the invention. The assembly 200 generally includes two components: a driver 210 and a converging nozzle 220. “Converging” in this sense simply means that the nozzle has a wall 224 that has a first larger diameter, D1 _(Nozzle), at a first end that is attached with seal 221 to the driver and a second larger diameter, D2 _(Nozzle), at a second end or at the muzzle 228. The wall seal 221 in most embodiments is preferably a substantially airtight seal which may be achieved with mechanical techniques such as fasteners without or without gaskets or other sealing members placed between the nozzle 220 and the driver 210. The nozzle 220 is shown to be a frustum or to be frustaconical in shape with the muzzle 228 generally being planar with an opening or outlet (as shown in FIG. 4). In other embodiments not shown, the nozzle 220 may be more tubular or cylindrical in shape (i.e., not be convergent as shown but instead more like a rifle barrel). The nozzle wall 224 defines a chamber or bore (as shown in FIG. 3) in which air is provided, quickly pressurized by the driver 210 during firing or discharging, and a projectile is formed as air is expelled at he muzzle or nozzle end 228. The nozzle wall 224, in this regard, has a wall thickness that when combined with the first and second diameters of the nozzle ends and length, L_(Nozzle), defines the volume of the chamber or bore of the nozzle 220. The nozzle 220 may be formed of metal, plastic, or other durable and pressure resistant materials and the wall thickness is typically less than 0.5 inches and more typically in the range of about 0 to 0.125 inches.

In the illustrated embodiment, the nozzle 220 is a converging nozzle. The amount of the convergence is defined by the angle θ that basically defines the slope of the wall 224 from it larger diameter end to the muzzle 228. The convergence angle, θ, may vary to practice the invention and achieve differing results; however, in some preferred embodiments, the convergence angle, θ, is less than about 45 degrees, more preferably less than about 20 degrees, and in particular embodiment is selected from the range of 5 to 10 degrees. With the convergence defined, another parameter of the nozzle 220 that needs to be chosen is the length, L_(Nozzle), of the nozzle 220 as measured from the two ends along the central axis of the bore or chamber. Experiments performed by the inventor have shown that the projectile results vary significantly with varying nozzle lengths, L_(Nozzle). However, the results have shown that generally the nozzle 220 should be selected to have a length, L_(Nozzle), that is chosen to suit the size of the driver 210. For example, the size of the driver 210 in embodiments may be expressed as the diameter of the frame or basket 214 at the point (i.e., the suspension) where the flexible membrane, cone, or diaphragm is attached. In FIG. 2, the membrane or cone diameter at this sealing point 221 can be thought of as being somewhat less than the larger diameter of the nozzle, D1 _(Nozzle). With this assumption in mind, the nozzle length, L_(Nozzle), is generally selected to be about 50 percent smaller to 50 percent larger than the membrane diameter. Of course, useful effects may be achieved with other nozzle lengths, L_(Nozzle), and the invention is not limited to this range of nozzle lengths. For example, the diameter of larger diameter of the nozzle 220, D1 _(Nozzle), may be about 16 inches and the diameter of the membrane may then be 14 to 15 inches or less. Using a membrane or cone diameter at the seal 221 of about 14 inches, the nozzle length, L_(Nozzle), is selected from the range of about 7 inches to about 21 inches. In one working embodiment of the assembly 200, the diameter of the membrane 218 (or, more accurately, of the distance across the basket or frame 214 at the point where the membrane or cone is attached to the suspension of the driver) at the seal 221 is in the range of 13 to 16.5 inches and the nozzle length is about 13 inches. Restating this relationship, the nozzle length is typically selected from the range of about 0.5 times the membrane diameter at or near the seal 221 to about 1.5 times this membrane diameter. This relationship will also likely vary with the about of excursion or throw that is provided by the driver 210 (in the above example, the excursion was about 2 inches in the forward direction) and the convergence angle, θ, of the nozzle wall 224 (in the above example, the convergence angle, θ, was between about 5 and 10 degrees) as well as the size of the outlet or opening in the muzzle (as discussed with reference to FIG. 4).

The driver 210 is configured to respond to control signals provided on connection 217 to respond (e.g., in milliseconds) by driving or moving a flexible membrane or diaphragm 218 through an excursion into or toward the nozzle 220, which causes a volume of air in the nozzle chamber or bore to be displaced. This rapid movement of the diaphragm or cone 218 causes the air in the nozzle chamber to be pressurized and for a similar volume of air to be expelled out the muzzle 228 as a projectile. The cone or membrane 218 is positioned or supported within a basket or frame 214 such that it can move or vibrate freely. The movement or vibration of the cone 218 through its excursion is caused by the movement of a coil or voice coil 216 through which the electrical control signal is transmitted via connection 217 (and amplifier often provided in an assembly 200), and the coil 216 may be connected to a central portion of the cone or membrane 218 or contact the membrane 218 to force it to move with the coil 216. A magnet is provided in housing 212 such that the coil 216 moves in response to the electrical signal passing through the coil 216.

In some embodiments, these components of the driver 210 are provided by using an audio speaker driver. Specifically, the driver 210 may be provided with an off-the-shelf woofer or subwoofer. In one particular embodiment, the driver 210 is a 10-inch, 12-inch, or 15-inch subwoofer but other sizes may be utilized to practice the invention. The power rating of the driver or subwoofer 210 may also be varied to practice the invention and may be 500 to 1000 or more Watts in some cases to provide desired force or power to effectively displace air in the nozzle 220. The throw or excursion is also preferably selected to be relatively large so that the cone or diaphragm 218 of the driver 210 displaces a larger volume of air when it flexes through its throw in response to the audio signals or electrical control signals provided at connection 217. In some cases, the excursion of the driver 210 may be 2 to 4 inches or more overall or 1 to 2 inches or more in each direction (i.e., in response to a positive signal and to a negative signal on connection 217 from the controller and/or amplifier not shown in FIG. 2). Of course, the driver(s) or loudspeaker(s) used to practice the invention are not limited to a particular size, capacity, or manufacturer. However, in one implementation, the driver is a woofer and is from the THUNDER® 9500 series, such as the T9515-44 model with a recommended power rating of 500 to 1000 Watts RMS and a diameter of about 13 to 14 inches adjacent the mounting face for seal 221 to nozzle 220 (sometimes listed as a cut out diameter for a woofer or speaker driver), and available from MTX® Audio (see, www.mtxaudio.com for product and purchasing information).

Significantly, this representative subwoofer is designed to provide air displacement of over 130 cubic inches, which can be used to pressurize the air to create a relatively large projectile that moves at slower speeds or more preferably a smaller projectile (e.g., a projectile with a volume of much less than 130 cubic inches) that moves at a high velocity when forced through a nozzle outlet at the muzzle 228 that is much smaller than the diaphragm diameter. Again, a wide range of nozzle openings and sizes may be used but the inventor has found that a reduction in the range of 50 to 90 percent or more produces a useful projectile effect. In the above particular embodiment, if the diaphragm diameter is about 13 inches, the opening in the muzzle may be selected to have a diameter or outer dimension in the range of about 6.5 to 1.3 inches or smaller to achieve a high speed, air projectile, and in one embodiment, a circular hole of about 2 inches in diameter has proven effective. Additionally, the control signal typically will be provided in the frequency response range of the driver, e.g., for the exemplary subwoofer the audio wave or pulse may be provided in the range of about 30 to 150 Hertz. The full wave may be used to in effect draw the cone or diaphragm 218 back (or cock it) and then send it through the full excursion or throw (e.g., of 4 inches in the above example), or, alternatively, just the forward portion of the wave or signal may be used to cause the cone 218 to move its at rest or neutral position into the nozzle chamber (e.g., move about 2 inches along the central axis of the driver 210 and nozzle 220). Again, the control provided by the use of the quick response, electrical driver 210 allows significant control over the timing and size of the projectile created by the assembly 200 and the waves (e.g., audio signals produced by an audio tone generation program that are converted into electrical control signals and amplified by an amplifier connected to connections 217) may be shaped in a variety of ways, have differing durations, have differing frequencies and magnitudes, and other characteristics to achieve desired results.

FIG. 3 illustrates an air projectile assembly 300 similar to assembly 200 and that, as with assembly 200, may be used in the system 100 (such as for driver 144 and nozzle 146 with amplifier 142). The assembly 300 is shown with portions cutaway to provide a better view of all the components of the assembly 300. As shown, the assembly 300 includes a driver 310 that is connected to a nozzle 320. The nozzle 320 includes a side wall 324 that is connected at a larger end to the driver 310 such as at or near the suspension 354 and adjacent the diaphragm 350. The side wall 324 extends from this larger diameter first end to a second end or muzzle 328, which typically has smaller diameter such that the nozzle 320 is a converging nozzle. The side wall 324 includes an inner surface 325 that defines a bore or chamber 329 of the nozzle 320. The surface 325 it typically provided as a smooth surface although some embodiments may include rifling or other texturing to achieve a desired result. The bore or chamber 329 defines the volume of air (or other gas) that is pressurized when the diaphragm 350 moves through is throw or excursion, and the muzzle 328 typically is a planar member with a smaller opening such that the displaced air is not simply pushed out the muzzle 328 but instead the air in the chamber 329 becomes pressurized due to the rapid movement of the diaphragm and then a projectile or fraction of the displaced air is forced out of the muzzle as a projectile as pressure is relieved in the chamber 329.

The driver 310 is shown to take the form of a loudspeaker driver such as a woofer (or a tweeter or midrange). The driver 310 includes a housing 312 in which a magnet 313 is rigidly positioned such that is does not move. The driver 310 further includes a structural frame or basket 314 attached to the housing 312 to provide a stationary or fixed mounting frame for a flexible spider or bellows 315 that is attached to the voice coil 318, which in turn is connected to wiring or electrical connections 317. A dust cap 319 is provided over the coil 310 and provides a connector or contact point to a flexible cone or diaphragm 350. The diaphragm 350 generally takes the shape of a dome, a cone, or a frustaconical shape, but some embodiments may have a relatively planar diaphragm 350 with the shape not typically being limiting as the displacement caused by the coil 318 is the more significant feature of the operation of assembly 300 (and may in some cases be a dome or diaphragm that extends out instead of tapering in as shown in FIG. 3). The diaphragm 350 is also supported by a suspension 354 that is attached to the frame or basket 314, and the nozzle wall 324 is attached (e.g., sealed) to the frame or basket 314 near or adjacent to the suspension 354.

The cone or diaphragm 350 is flexible and may be made of a variety of materials such as paper, plastic, or metal and is attached at it wide end to the suspension 354. The suspension or surround 354 is a rim of flexible material that allows to the cone 350 to move relative to the basket or frame 314 (e.g., a metal, plastic, or other structural material frame/structure). The smaller end of the cone or central portion of the diaphragm 350 is connected to the voice coil 318 such as at or with optional dust cap 319 (e.g., some embodiments will include a solid or contiguous diaphragm rather than one with a central hole scaled to or connected to the dust cap/voice coil). The coil 318 is able to move back and forth along the central axis of the driver 310 due to its attachment to the cone 350 and to the flexible spider 315. During operation, the driver 310 operates based on electromagnetic processes as the voice coil 318 is a coil of wire wrapped about a piece of magnetic material such as iron. Running an electric control signal through connections 317 and the coil 318 creates a magnetic field around the coil 318 magnetizing the metal it is wrapped about, and a control signal on line 317 can be used to provide a biasing or switching signal that fluctuates between a positive and a negative charge to cause the voice coil 318 to move in a forward or backward direction because it is positioned in a constant magnetic field provided by permanent magnet 313 and the two magnets attract and repel each other as the control signal in coil 318 is varied or changed from positive to negative (e.g., the coil moves back and forth causing the diaphragm 350 to act like a piston in the bore or chamber 329 of nozzle 320). More generally, it is a coil of wire in a magnetic gap that provides the driving force for most loudspeakers. In some embodiments, though, piezoelectrically-driven loudspeakers may be utilized.

As shown, a positive signal (for example but not a limitation) may be used to move the central point of the diaphragm 350 or the dust cap 319 in this example from a first position or at rest position “Pos. 1” to a second position “Pos. 2” by moving it through a throw or excursion “Throw A,” A negative signal may likewise be used to cause the diaphragm 350 to move to a third position “Pos. 3” by moving through a throw or excursion “Throw B” in the opposite direction. In some embodiments of the invention, a simple sine or square wave with a positive portion and a negative portion is used to cause the diaphragm to move from the first position “Pos. 1” to the second position “Pos. 2” and then to the third position “Pos. 3.” In other cases, only the positive portion of the sine or square wave is used as the control signal on connection 317 to cause the voice coil 318 and attached diaphragm 350 to move from the first position “Pos. 1” to the second position “Pos. 2” by moving through excursion or throw “Throw A” (which may be up to 2 inches or more for some speaker drivers 310). The driver 310 may take other forms to practice the invention and may be thought of as one means for driving the cone/diaphragm 350 in response to a control signal or to an amplified audio or control signal (e.g., from controller 114 of FIG. 1). The assembly 300 may be provided in an enclosed box or container but for proper operations it is preferable an air vent or opening be provided to allow the air in the nozzle to be replenished. This may be achieved simply by leaving the muzzle open to ambient air or it may be supplemented by providing a vent in the nozzle wall 324 (e.g., with a one-way check valve that only allows flow into the nozzle chamber 329) such as a near the suspension 354 (e.g., near the larger end of the nozzle 320).

Although not shown in FIGS. 1-3, the air projectile assemblies of the invention may include devices to process the control signal such that it is provided in a frequency that is useful to the driver 144, 210, or 310. For example, the drivers may be audio speaker drivers that are typically most responsive to particular frequency ranges. The control signal may be configured or selected to be in the range of the driver or the control signal may be filtered or processed by a crossover or similar device such that the control signal delivered to the driver (such as by the amplifier or by the crossover device when the crossover is provided between the amplifier and the driver as is common with speaker drivers) is within the correct frequency range. For example, a woofer may be used for the driver, and, in this example, a crossover may be used to provide a low frequency control signal to the driver (e.g., less than about 150 Hertz or the like).

In some embodiments, the muzzle end of the nozzle is generally planar with a smaller opening or outlet through which the air or other gas projectile is discharged, expelled, or “shot.” FIGS. 4A-4C illustrate some exemplary nozzles with differing outlet configurations or shapes. FIG. 4A shows a nozzle 420 with a side wall 424 that converges from a wider first end to a second end or muzzle 428 having a smaller diameter, D2 _(Nozzle). The muzzle 428 is typically planar but differing arrangements such as semi-spherical may be used in some embodiments. More significantly, the muzzle 428 includes a smaller area outlet 450. The outlet 450 is shown to be circular and to have a diameter, D_(Outlet), that is preferably selected to be smaller than the diameter of the muzzle, D2 _(Nozzle), and of the diaphragm, with a reduction from the diaphragm of 50 to 90 percent or more being useful in many cases. For example, the outlet 450 may be positioned on the central axis of the nozzle 420 (although this is not a requirement and the number of openings 450 may be also be 2 or more to produce multiple projectiles) and have a diameter, DOutlet, that is selected to be chosen to be less than about 6 inches and in some cases in the range of about 1 to 4 inches. Again, as discussed above, the size of the opening may be chosen to be proportionate to the size of the diaphragm and for example, if the diaphragm is about 13 inches in diameter it may be useful to have an outlet selected to have a diameter, D_(Outlet), in the range of 1 to 3 inches or about 2 inches. But, again, good projectile results can be achieved over a large range of outlet sizes and shapes with these simply being useful examples of how the invention may be practices.

In FIG. 4B, a nozzle 460 is shown with a converging side wall 464. The nozzle 460 has a muzzle 466 that is generally planar with an oval or elliptical outlet or opening 468. Numerous other shapes may also be useful, and FIG. 4C shows a converging nozzle 470 with a side wall 474 extending from a first end to a second end or muzzle 476 that encloses the nozzle's chamber or bore except for an opening or outlet 478 that is shown to be diamond shaped. The projectiles may differ somewhat with differing outlet shapes but generally it is expected that the size (or area) of the opening is a more limiting factor than its exterior shape. Hence, it may be useful for the opening to be defined as having an area selected based on the area of the diaphragm (or its radius at the mounting to the frame or basket). For example, the area of the opening may be selected to be a small fraction of the area of the diaphragm (e.g., a fraction similar to that achieved when the outlet is circular and the diameter is 50 to 90 percent smaller than the diameter of the diaphragm). However, nearly any shape may be used for the outlet with a circular, elliptical, or diamond (or other polygon) being just examples.

As shown in FIG. 1, the air projectile assemblies of the present invention are particularly well suited for use within an attraction, game, or special effect system to produce air projectiles promptly in response to a control signal but with significantly less noise and size/space requirements relative to typical air cannons. FIG. 5 shows a method 500 of using and/or operating an air projectile assembly according to the present invention such as may be implemented by operating the system 100 of FIG. 1 (which, in turn, may use the assemblies 200 and 300 of FIGS. 2 and 3 with muzzle configurations shown in FIGS. 4A-4C). The method 500 starts at 504 typically with planning what types of projectiles are needed such as what size the projectiles should be, how fast and far the projectiles need to travel (such as within a second and 1 to 5 feet or larger distances such as 10 to 30 feet or more), whether the projectiles should strike the same location repeatedly or be directed more randomly, and whether simple air should be used or other gases or additional features such as scent or visibility (e.g., smoke) is desired for the projectiles. With these design and operating parameters defined, the method 500 continues at 510 with providing a projectile assembly in or near a target environment (e.g., one in which target objects or guests will be located). The assembly is connected to a controller that provides electrical control signals (e.g., such as stored audio signals or the like) and the nozzle is targeted to a particular location in the target environment (e.g., to strike or pass near a guest or to strike or pass an object that is to be vibrated or otherwise affected by the air projectile).

At 520, the method 500 includes storing one or more control signals in memory of the attraction ride or server. For example, an audio signal generator may be used to produce one or more signals that can be stored in memory. For example, if the assembly includes a woofer a sine or square wave with a frequency of 30 to 150 Hertz or the like may be created. The duration of the forward or positive current may be set at a duration of less than about 100 milliseconds such as less than about 30 milliseconds (e.g., about 15 to 17 milliseconds), and this forward or positive current portion of the wave may be used by the controller as the control signal (e.g., to cause a driver to move a flexible membrane through a positive or forward excursion into or toward the chamber of the nozzle). In other embodiments, the game or attraction software itself acts to generate sound or other electrical signals that are fed by the game controller (with or without further processing) to the driver as control signals. In these embodiments, the action or event within the attraction or game may result in differing control signals being sent to the driver (or this may be done by the controller retrieving differing control signals from memory based on the triggering event or occurrence).

At 530, the method 500 continues with determining whether a triggering event has occurred and if not, the method 500 loops until such an event is identified. In a game example, the triggering event may be an occurrence in the game such as a ball or other object flying toward the player. In an attraction, the triggering event may be reaching a frame in a movie/film or audio clip, a car or guest being detected to have reached a particular location, or the like. If the triggering event has occurred, the method 500 continues at 540 with retrieving (or generating as discussed above) a control signal such as from system or server memory. At 550, the control signal is transmitted to the air projectile assembly. The signal may be amplified at 560 (such as to a point within the power range of the driver, e.g., between 500 and 1000 Watts when the driver is a woofer with a rating of 500 to 1000 Watts RMS). The amplified signal is then used at 570 to operate the driver to produce a projectile or to shoot/discharge an air projectile at the targeted guest, object, or target. The process 500 either continues at 530 with waiting for a next targeting event or ends at 590. As discussed with reference to FIG. 1, the targeting of the projectiles may be made to appear “random” by maintaining the time between or discharge delay less than a particular time period (e.g., less than about 10 to 20 seconds in some cases). As a result of this short discharge delay (or relatively short time between discharges), the nozzle may not be completely refilled or may still have turbulence or moving air from the last discharge that causes the next projectile to be shot or expelled off of the central axis of the nozzle (or not perpendicular to the muzzle or a plane passing through the outlet).

Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed. For example, the projectile assemblies illustrated in the figures showed the use of a single driver, but the concepts described are readily extended to cover the use of 2 to 5 drivers to produce an air pulse or projectile at an outlet (e.g., use two or more drivers of the same or differing size to combine their outputs into a nozzles to create more powerful pulse than achievable with one of these drivers). Likewise, the nozzles were generally shown to include a single outlet and to be converging, but the inventive concepts include a nozzle with two or more openings in the outlet that produce two or more projectiles concurrently or substantially concurrently that are directed in the same direction or in two different directions. Additionally, the “nozzles” may include or be formed by a housing or manifold on which one, two, or more drivers or loudspeakers are mounted with the housing defining an inner chamber in which air is displaced and/or pressurized quickly and discharged from one or more openings or outlets from the inner chamber and housing (with or without convergence).

For example, FIG. 6 illustrates one air projectile assembly 600 of the present invention that illustrates one arrangement of multiple drivers or loudspeakers 630. As shown, the five drivers 630 are mounted on a manifold or housing 610, which may be a cube shape with 6 sides, be a sphere, or many other shapes/configurations for providing mounting surfaces for two or more drivers 630. The manifold or housing 610 defines an inner chamber or interior space that is generally a cube but other shapes may be defined by the housing 610. In the assembly 600, drivers 630 are mounted on five sides or walls of the manifold or housing 610 while an outlet plate 620 with an opening or exit 624 through which projectiles are discharged by operating one or more of the drivers 630. The inner chamber of the manifold or housing 610 along with the outlet plate 620 define a nozzle that, in the illustrated embodiment is non-converging. In other embodiments not shown, the plate 620 may be replaced with a converging nozzle similar to those shown in FIGS. 1-5 (e.g., each outlet 624 may be provided on a converging nozzle).

Generally, the drivers 630 are operated in unison or concurrently so as to increase the electrical power that can be input and/or to increase the volume of air/gas displaced by the drivers 630, which may result in a larger projectile and/or a projectile that is discharged at a higher velocity. Of course, the drivers 630 may, in some cases, be operated individually or in other combinations such as one driver 630, than two drivers 630, than three drivers 630, and other combinations to achieve desired outputs or projectiles (e.g., projectiles of differing size, speed, and/or direction (in some cases)). The characteristics of produced projectiles will vary with the interior configuration of the manifold 610 (e.g., the “nozzle” defined by the inner chamber of the manifold 610 when combined with the plate 620 and outlet 624), the displacement capabilities of the drivers 630, the control or input waveform or control signal applied to the drivers 630, the opening 624 size and shape, and other physical and operating parameters such as time between firings and the like as discussed above.

Further, the manifold 610 may be modified to include more than one opening or outlet 624 on the plate 620 or in differing locations to provide projectiles that travel in differing directions. When multiple openings are provided in the manifold 610, mechanisms may also be provided for blocking or closing one or more of such openings to discharge projectiles selectively from one or more of the openings (e.g., a shutter or other mechanism for selecting which of the openings are used to create air projectiles). In some cases, it is desirable to vary the size and speed of the projectiles by varying the size of the opening in the manifold or nozzle, and this may be achieved manually by changing the outlet diameter (or nozzle bore) such as by replacing the plate 620 in assembly 600. In other applications, the size of the opening in the plate 620 or a nozzle is achieved with mechanisms that can be controlled and operated remotely such as devices similar to those used in cameras to adjust the amount of light entering the camera, devices that simulate an iris of an eye, and the like. Yet further, the drivers 630 may be positioned differently, such as all provided substantially opposite the outlet plate 620, and/or may be provided in differing numbers or with varying size or operating characteristics than shown. 

1. An air projectile assembly, comprising: a driver with a flexible diaphragm and means responsive to an electrical control signal to displace the flexible diaphragm from a first position to a second position; and a nozzle connected to the driver having an inner bore that converges from a first size at a first end proximate to the flexible diaphragm to a second, smaller size at a second end distal to the flexible diaphragm.
 2. The assembly of claim 1, wherein the second end comprises a planar muzzle extending perpendicular to a central axis of the nozzle bore, the planar muzzle comprising an outlet with an area at less than about one third of an area of the diaphragm.
 3. The assembly of claim 1, wherein the second end comprises a circular outlet having a diameter less than about one half a diameter of the diaphragm as measured across an opening of the driver adjacent the nozzle.
 4. The assembly of claim 3, wherein the diaphragm diameter is less than about 24 inches and the circular outlet diameter is selected from the range of about 0.25 to about 12 inches.
 5. The assembly of claim 1, wherein the means responsive to the electrical control signal displaces the flexible diaphragm to the second position in less than about 100 milliseconds.
 6. The assembly of claim 5, wherein the means responsive to the electrical control signal displaces the flexible diaphragm to the second position in less than about 20 milliseconds and the first position is 0.5 to 4 inches from the second position.
 7. The assembly of claim 5, wherein the means response to the electrical control signal comprises an audio speaker driver and the flexible diaphragm comprises a cone of the audio speaker driver.
 8. The assembly of claim 7, wherein the assembly further comprises a power amplifier providing the electrical control signal at a power level within a power rating range of the audio speaker driver, the audio speaker driver comprising a woofer.
 9. The assembly of claim 1, wherein the bore converges from the first end to the second end with a slope or convergence angle of less than about 20 degrees.
 10. The assembly of claim 9, wherein the nozzle has a length selected from the range of about 50 percent of a diameter of the flexible diaphragm to about 150 percent of the diameter of the flexible diaphragm.
 11. An apparatus for discharging air projectiles, comprising: a driver comprising a flexible membrane and responsive to an electrical signal to move the membrane from a first position to a second position in less than about 100 milliseconds; and a nozzle attached to the driver such that the movement of the membrane causes air in an inner chamber of the nozzle to be displaced, the nozzle further comprising a muzzle distal to the driver with an outlet through which an air projectile is discharged in response to the air being displaced in the inner chamber by the membrane.
 12. The apparatus of claim 11, wherein the electrical signal is an audio signal with a duration of less than about 20 milliseconds and the driver comprises an audio speaker driver with a forward throw that moves the membrane from the first position to the second position in less than about 20 milliseconds.
 13. The apparatus of claim 11, wherein the nozzle is a converging nozzle with a convergence angle of less than about 20 degrees.
 14. The apparatus of claim 11, wherein the membrane has an outer diameter and the nozzle has a length selected from the range of about 50 percent of the membrane outer diameter to about 150 percent of the membrane outer diameter.
 15. The apparatus of claim 14, wherein outlet is circular with a diameter selected from the range of 10 to 30 percent of the membrane outer diameter.
 16. A system for selectively generating an air projectile that travels into a target environment, comprising: an air projectile assembly comprising a power amplifier for amplifying electrical control signals, a driver with a flexible membrane responding to the amplified electrical control signals by moving a central portion of the membrane to displace a volume of air in contact with the membrane, and a converging nozzle with a chamber containing the displaced volume of air and with a muzzle having an opening smaller than a diameter of the flexible membrane directed toward the target environment; and a controller selectively transmitting the electrical control signals in response to triggering events to the power amplifier, whereby air projectiles are expelled from the muzzle opening based on each of the electrical control signals.
 17. The system of claim 16, wherein the driver is an audio speaker driver and the electrical control signals comprise audio signals.
 18. The system of claim 17, wherein at least some of the electrical control signals differ in configuration and duration and wherein the air projectiles produced by the air projectile assembly vary for differing ones of the electrical control signals.
 19. The system of claim 16, wherein the controller transmits successive ones of the electrical control signals with a time between transmittal below a predefined time period such that corresponding successive ones of the air projectiles are discharged along differing target lines from the muzzle opening into the target environment.
 20. The system of claim 16, wherein the triggering events comprise occurrences in a video game, wherein at least one of the expelled air projectiles follows a target line toward a guest or object in the target environment, and wherein the guest or object is greater than 5 feet away and the at least one of the expelled air projectiles reaches the guest or object in less than about one second.
 21. An apparatus for discharging gas projectiles, comprising: a manifold with a side walls defining an inner chamber, wherein a discharge opening is provided in one of the side walls providing a passage for gas to and from the inner chamber; and two or more drivers mounted on the side walls of the manifold comprising a flexible membrane and a mechanism for moving the membrane from a first position to a second position in response to a control signal to displace a volume of the gas in the inner chamber and discharge a projectile formed of the gas from the discharge opening.
 22. The apparatus of claim 21, wherein the drivers comprise loudspeakers and the control signal comprises an audio signal.
 23. The apparatus of claim 21, further comprising a mechanism for adjusting a size of the discharge opening in response to a control signal.
 24. The apparatus of claim 21, wherein the manifold comprises an additional discharge opening in one of the side walls.
 25. The apparatus of claim 21, wherein the second position of the membrane is more proximate to the inner chamber than the first position.
 26. The apparatus of claim 25, wherein the mechanism moves the membrane from the first to the second position in less than about 20 milliseconds and the second position is at least about 0.5 inches from the first position.
 27. The apparatus of claim 21, wherein the manifold comprises six of the side walls and the inner chamber is generally cubic in shape and wherein the apparatus comprises at least 3 of the drivers mounted on the side walls. 